In order to mitigate the problem of back-corona discharge in electrostatic precipitators, method and apparatus are provided for energizing the precipitator electrodes with repeated bursts of high voltage electrical pulses, superimposed upon a direct current voltage level. Additionally, the voltage of the pulses in a single burst is increased from each pulse to the next pulse during the time period that the pulse burst is applied. The effect of the ramping of the pulse burst voltage is to increase the average electric field and ion density during the pulse burst. The result is substantially higher particle charging which leads to improved particle charging collection efficiency. Moreover, in addition to eliminating the back-corona discharge problem which particularly occurs in the collection of high resistivity dust particles, the present method and apparatus for precipitator energization achieves the same advantages as so-called board pulse powering precipitator methods, without, however, the concomitant circuit cost associated with high voltage and high power switching devices.

Method and apparatus for ramped pulsed burst powering of electrostatic precipitators

This paper numerically analyzes corona power loss associated with wire-duct electrostatic precipitators. The finite-element method is used to solve Poisson's equation and a modified method of characteristics is used to satisfy the current continuity condition. The two methods are repeated iteratively to obtain a self-consistent solution of the describing equations. The effectiveness of this approach is tested by comparing the computed results with previously obtained experimental and calculated values. The agreement with experimental results is found to be satisfactory.

A combined algorithm based on finite elements and a modified method of characteristics for the analysis of the corona in wire-duct electrostatic precipitators

This paper numerically analyzes corona power loss associated with wire-duct electrostatic precipitators. The finite-el- ement method is used to solve Poisson's equation and a modified method of characteristics is used to satisfy the current continuity condition. The two methods are repeated iteratively to obtain a self-consistent solution of the describing equations. The effective- ness of this approach is tested by comparing the computed results with previously obtained experimental and calculated values. The agreement with experimental results is found to be satisfactory. Index Terms—Corona power loss, finite-element method, method of characteristics, precipitators, space charges.

A Combined Algorithm Based on Finite Elements and a Modified Method of Characteristics for the Analysis of the Corona in Wire-Duct

In electrostatic precipitators (ESPs) the separation of particles from flue gases is based on electrical means. The separation process can be divided into five essential steps which are schematically illustrated in Figure 3.1: 

1.

generation of charge carriers (section 3.2);




2.

charging of the particles (section 3.3);




3.

deflection and separation of the particles (sections 3.4, 3.5);




4.

dust deposition (section 3.6);




5.

dust removal (section 3.7).






In most applications the steps are not as isolated as represented here, but the steps can happen all in one operational section. These are the so-called single-stage precipitators, which are the most important configurations for industrial processes (Figure 3.2a). In so-called two-stage precipitators steps 1/2 are executed separately from steps 3/4/5, i.e. in the first stage the ions are produced and the particles are charged while in the second stage the particles are collected and removed (Figure 3.2b). The two-stage configur- ations are only used in small-scale applications as, for example, clean room technology. Since single-stage precipitators have a far greater industrial significance than two-stage ESPs, the discussions will be confined to the first. However, most of the presented subjects and equations can be equally applied to two-stage configurations.

Basic and theoretical operation of ESPs

The use of pulse powering for electrostatic precipitators has shown several advantages but the underlying physics has been insufficiently understood to allow any optimization. A numerical model has been assembled which allows the controlling corona process to be simulated in both time and space to permit estimation of the ion densities and field distributions to be expected for a wide range of transient electrical parameters and gas properties. Supporting laboratory measurements have been undertaken under dc and pulse conditions both to verify the simulation and to provide corona spot density data not readily obtainable by other means.

Simulation and measurement of corona for electrostatic pulse powered precipitators

Increased research in electrostatic precipitation has resulted in the emergence of promising new technologies. In a new design concept already widely used in Japan, the precipitator duct spacing is increased from the traditional 200-300 mm up to 400-600 mm, and the precipitator voltage is raised correspondingly, with precipitator performance remaining almost unchanged for the same precipitator volume and the same gas flow. For suitable applications, this design results in reduced installation costs and easier maintenance. Various devices for precharging of high resistivity dust now under development improve particle charging and thereby enhance precipitator performance. Pulse energization improves the performance of precipitators collecting high resistivity dust by improving particle charging and current distribution and allowing regulation of the precipitator current independent of precipitator voltage.

Helge H. Petersen

Papers

New Trends in Electrostatic Precipitation: Wide Duct Spacing, Precharging, Pulse Energization